Mass reduction in vehicle parts and components lowers the rate of the vehicle's fuel consumption. Thus different materials are considered to form vehicle structure which may be lighter in weight than steel or metal, but yet provide the sufficient structural strength for body support. In particular, it is known to replace metal frames for vehicle components such as seat assemblies with polyurethane, or polypropylene.
Polypropylene has sufficient compression and tensile strength to replace the metal in the manufacture of the seat back assembly frame. Indeed, some vehicle seat backs have done so. Expanded polypropylene (EPP) is generally polypropylene that has been expanded using gas injection during the molding process. EPP has a lower density than polypropylene and thus weighs less than the same volume of polypropylene. Thus it remains desirable to reduce the mass of a seat back assembly by using a frame than is lighter than metal, but yet has sufficient structural integrity so as to withstand the load associated with vehicle operation.
Another aspect of vehicle design is maintaining the structural integrity of a vehicle component during normal operating conditions. In the course of normal vehicle operation, EPP structure may become damaged due to the load. For instance, the interior of a vehicle trunk may experience a load due to articles contained therein shifting during vehicle operation.
In sedan type vehicles, the seat back assembly may back up to the trunk space. As often the case, the trunk space may contain articles such as groceries and the like. These articles may shift while the vehicle is being driven. In some cases, such as a quick stop, the articles may be forced into contact with the seat back assembly. Such a load may damage the seat back assembly.
It is known to protect the seat back assembly from such damage by using a panel made of hardened resin, or metal. In other instances, the seat back frame may be composed of metal and include reinforcement structures such as a bar. In yet another example of a seat back reinforcement is the use of a rib on a panel of a seat back. The rib helps the panel maintain its structural integrity by providing added rigidity to the panel. However such seat assemblies require a substantial amount of mass or are costly to manufacture. Accordingly, it remains desirable to provide a seat assembly with minimal mass and relatively inexpensive to manufacture.